Proper use of beginBackgroundTaskWithExpirationHandler
background-thread, ios, multitasking, network-programming, objective-c
Solution
If you want your network transaction to continue in the background, then you'll need to wrap it in a background task. It's also very important that you call `endBackgroundTask` when you're finished - otherwise the app will be killed after its allotted time has expired.
Mine tend look something like this:
- (void) doUpdate
{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
[self beginBackgroundUpdateTask];
NSURLResponse * response = nil;
NSError * error = nil;
NSData * responseData = [NSURLConnection sendSynchronousRequest: request returningResponse: &response error: &error];
// Do something with the result
[self endBackgroundUpdateTask];
});
}
- (void) beginBackgroundUpdateTask
{
self.backgroundUpdateTask = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
[self endBackgroundUpdateTask];
}];
}
- (void) endBackgroundUpdateTask
{
[[UIApplication sharedApplication] endBackgroundTask: self.backgroundUpdateTask];
self.backgroundUpdateTask = UIBackgroundTaskInvalid;
}
I have a `UIBackgroundTaskIdentifier` property for each background task
Equivalent code in Swift
func doUpdate () {
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), {
let taskID = beginBackgroundUpdateTask()
var response: URLResponse?, error: NSError?, request: NSURLRequest?
let data = NSURLConnection.sendSynchronousRequest(request, returningResponse: &response, error: &error)
// Do something with the result
endBackgroundUpdateTask(taskID)
})
}
func beginBackgroundUpdateTask() -> UIBackgroundTaskIdentifier {
return UIApplication.shared.beginBackgroundTask(expirationHandler: ({}))
}
func endBackgroundUpdateTask(taskID: UIBackgroundTaskIdentifier) {
UIApplication.shared.endBackgroundTask(taskID)
}
Problem
I'm a bit confused about how and when to use `beginBackgroundTaskWithExpirationHandler`. Apple shows in their examples to use it in `applicationDidEnterBackground` delegate, to get more time to complete some important task, usually a network transaction. When looking on my app, it seems like most of my network stuff is important, and when one is started I would like to complete it if the user pressed the home button. So is it accepted/good practice to wrap every network transaction (and I'm not talking about downloading big chunk of data, it mostly some short xml) with `beginBackgroundTaskWithExpirationHandler` to be on the safe side?